Sybrina Fulton suggested officers had leaked details about the 17-year-old's poor school record in order to deflect attention away from their failure to arrest George Zimmerman over his death in Sanford, Florida last month.

"They've killed my son, and now they're trying to kill his reputation," she said.

Trayvon's father, Tracy Martin, added: "We take pride in our kids and it tears me apart to sit here and listen to the slander they are giving my son.

"Even in death, they are still disrespecting my son. I refuse to let them assassinate my son's character."

The case led to protests across America after Mr Zimmerman, whose father is white and mother Hispanic, was told he faced no charges due to Florida's controversial Stand Your Ground self-defence law, which allows people to attack if they believe they are in danger.

Trayvon's parents said the shooting would have been handled differently had their son been white. Prosecutors are reviewing why Mr Zimmerman, 28, was not charged and a decision is expected next month.

Reports have now emerged about Trayvon's school record, including a series of suspensions and a suggestion he was suspected of burglary, leading to criticism from his parents.

Officials confirmed that the boy had been caught scrawling graffiti on a locker at Krop High School in Miami, and when his bag was searched he was found with items of women's jewellery and a screwdriver, which was confiscated as a possible "burglary tool".

He had earlier been suspended for "truancy," and was serving another temporary exclusion from the school, after traces of marijuana were found in his bag, when he was killed.

Mrs Fulton and Mr Martin, who are separated, say the school never told them about the jewellery found in Trayvon's bag, and no suggestion that he had been involved in burglary was ever raised with them.

They claim that the truancy suspension was given because Trayvon had been late to class, and that his attendance record was good.

Mr Martin said: "The question should not be why was he suspended from school, it should be why did this man kill him in cold blood."

It was during the latest suspension that Trayvon, who did not have a criminal record, went to stay with his father in Sanford, an area where he was not known to neighbours, and where Mr Zimmerman would later tell police he was acting suspiciously.

He had been on his way back from a shop where he had bought sweets for his little brother when he was challenged by Mr Zimmerman, who claims that Trayvon hit him first.

Several neighbours have disputed this version of events, saying they heard the boy screaming before a shot rang out. Trayvon's girlfriend, who he was on the phone to at the time, has claimed that he knew he was being followed and was frightened.

Meanwhile, Mrs Fulton's lawyer has confirmed that she is planning to trademark the phrases "Justice for Trayvon" and "I am Trayvon," which have become rallying cries for protesters and appear on merchandise related to the case.

Trademark attorney Kimra Major-Morris said Mrs Fulton wanted to safeguard intellectual property rights for "projects that will assist other families who experience similar tragedies," and would not be making a profit.